Although Lacy progressed through another stage of the concussion protocol on Thursday, according to coach Mike McCarthy, the rookie running back did not practice.

“The medical staff still feels like he has a good opportunity (to play),” McCarthy said Thursday. “So he has to practice tomorrow for us to be able to gauge him.”

If Lacy does not play against the Bengals, the Packers may be down to only two available backs -- James Starks and Johnathan Franklin -- because fullback John Kuhn (hamstring) also did not practice on Thursday. It’s a potentially dangerous position, because essentially Starks would be their only proven back. Franklin, a rookie fourth-round pick, has not played a snap on offense in the first two games.

The Packers could promote rookie Michael Hill from the practice squad, but would have to find a roster spot for him, and he has even less experience in their offense because he wasn’t signed until after training camp.

“If we have two, then nobody’s allowed to get hurt,” running backs coach Alex Van Pelt said Thursday. “I’m sure we’ll have a contingency plan if something were to happen.”

The last time the Packers went into a game with only two running backs, it was a borderline disaster. On Dec. 18, 2011 at Kansas City, the Packers had only Kuhn and Ryan Grant available. Grant had been effective (12 carries for 66 yards) but was nursing bruised ribs. Although he was able to finish the game, McCarthy basically abandoned the running game in a 19-14 loss.

“The preference is not go into the game with two running backs,” McCarthy said. “I did that one time in Kansas City, learned a hard lesson, especially when one of them was nicked going into that game. It hurt us in the second half. We’ll be much better prepared than we were two years ago in Kansas City.”

In other injury news, safety Morgan Burnett likely will miss his third straight game because of a hamstring injury.

“He’s coming along; it’s not the progress that I’m sure Morgan wants,” McCarthy said. “I think he’s going to be a long shot this week.”